I've been using Navmii (paid Navfree) for a month now. Before I had a tomtom.
Good points:
-choice of fastest, easy (non motorway or big A roads), or economical routing, and avoiding motorways.
-price
-easy to get to ipod music
-really good google search function
-speed camera add on seems accurate
Bad points:
-It has tried to take me down wrong way roads, and I expect that this is more common, as there are fewer users to record and log these problems, unlike tomtom.
-Muddled instructions: It annoyingly says 'take the next right onto the A123', when you are on the A123, and the turn off you need is the A1234.
Another significant killer of a shortfall is that you cannot plan a itinerary, which renders the app useless for me, as I like to go from A to B via C and D. There is no option for this, apart from driving to A, to C, then stop and put details of D in etc.
Trying to find a free or cheap sat nav app that has this function so I can plan my rideouts on my phone before I go.
I will jailbreak my phone soon, but I'm running 10.4.11 osx, and cannot sync my phone with my mac (where is the logic in that, for brand loyalty).
:-()
Will have another go with skobbler, but it does seem a bit basic. Real bummer there is no Garmin for UK/europe, or Motionx GPS drive, for iphone.